This invention relates to closures for containers and more particularly to the so-called "safety" closures which, once drawn into sealing engagement with the container, can be removed only by a special manipulative procedure which is beyond the capabilities of most infants and small children.
Various safety closures have been suggested by the prior art which are designed to make the removal of the closure much more difficult than in the case of conventional closures. Such safety closures are primarily used on containers which are designed to be "child-proof". Such closures require special manipulative techniques which are normally beyond the comprehension or physical ability of a child so that removal of the closure by children is extremely difficult and the danger of a child removing the closure and consuming the contents of the container is substantially reduced.
Such closures can be generally described as including a resilient sealing member which is compressed when the closure is drawn into the sealing position, a depending skirt portion adapted to fit over the neck of the container and which is adapted on the inner surface thereof, usually by threads, for engagement with the container to maintain the closure in sealing position on the container. In addition, the depending skirt portion normally carries one or more separate projections or lugs which are adapted to interengage with cooperating indentations or projections on the container for interlocking to prevent removal of the closure. These are maintained in their interlocking relationship by the upward urging of the resilient sealing member acting against the open end of the container, which sealing member is compressed when the closure is drawn into sealing relationship on the container. The closures are designed to be removed by downward pressure on the closure top which allows the closure to move downwardly resulting in a disengagement or unlocking of the corresponding projections or lugs or the closure from the indentations or projections on the container so that the closure can be removed in the conventional manner.
A significant problem encountered with the prior art safety closures is found in connection with the provision of separate projections or lugs on the closure particularly where the closure and container are threaded. Such projections or lugs, when engaged with corresponding means on the container are often of insufficient strength to withstand the shearing forces which may be encountered in an attempt to remove the closure from the container when it is in the locked position on the container and the closure is not properly manipulated to remove it in the proper manner. Thus, the projections or lugs may often be easily sheared resulting in elimination of the safety lock feature. Also, in many prior art designs, it is necessary that the lug or projection on the closure be of a resilient material so that the closure can be urged into its locked position. Such designs are unsuitable for use with metal, glass, rigid plastic and the like materials which are often desirable for use as a closure composition. Many of the designs incorporated in the prior art safety closures are such as to inhibit the sealing function of the closure so that a true fluid tight seal between the closure and the container is often not obtained.